The present invention relates generally to vehicular stability control. More particularly, the invention relates to a method for enhancing vehicle stability control.
In vehicle stability enhancement (VSE) systems, and some other chassis control systems, a significant effort during vehicle tuning may be devoted to the process of characterizing vehicle response in the yaw plane to the steering inputs. This may be accomplished by building look up tables that give steady state values of vehicle yaw rate, and sometimes lateral velocity for various steering angles and vehicle speeds. Since several values of speeds and steering angles have to be considered, the tables involve more than a hundred numbers, each of which has to be determined experimentally. This usually involves several days of testing, which has to be performed on a dry surface, thus being dependent on the weather conditions.
Another drawback of the look up tables is that linear interpolation is used between any two points defined in the table. This may lead to errors when the function approximated by piecewise linear segments is strongly nonlinear. Accordingly, it would be desirable to provide a relatively simple strategy that would permit one to determine the desired values from analytical expressions using vehicle parameter data, which are usually supplied by the vehicle manufacturer. In this way the desired values (of yaw rate and lateral velocity) could be continuously computed, or the look up table values could be determined by running a utility file on a computer. Only limited testing may be needed to verify the correctness of the model.
Therefore, it would be desirable to provide a strategy for enhancing vehicle stability control that overcomes the aforementioned and other disadvantages.
One aspect of the present invention provides a method of vehicle stability control. A rear axle cornering stiffness coefficient in a linear handling range is determined. A first understeer coefficient in a linear handling range is determined. A desired lateral acceleration is determined based on the first understeer coefficient. A second understeer coefficient is determined based on a limited magnitude of the desired lateral acceleration. A desired yaw rate is determined based on the second understeer coefficient. A desired lateral velocity is determined based on the desired yaw rate and the rear axle cornering stiffness coefficient. The rear axle cornering stiffness coefficient may be determined based on a cross-over lateral velocity. A front axle cornering stiffness coefficient in a linear handling range may be determined. The determined desired yaw rate, desired lateral velocity, and desired lateral acceleration may be transmitted to a vehicle control system.
Another aspect of the invention provides a computer usable medium, including a program, for vehicle stability control. The invention provides computer readable program code for performing the method steps described above.